First Startup
Wang 600 Minimal Assembly
The machine was assembled in a minimal state for first tests - MOS ROM attached but no printer or tape drive.
With power supplies tested and volt clamps in place one can load all the PCBs and attempt a first power-up with low risk. On first power up:
- voltages were stable, indicating no abnormal loads (eg shorted tantalums)
- keyboard lamps illuminated, and cleared when Prime was pressed
- display remained blank after Prime and Set PC
- display showed consistent garbage patterns after Verify or Record
Wang 600 after Record Prog
Wang 600 after Verify Prog
Wang 600 DCode3
While the machine is unable to run enough microcode to generate a display after Prime, the results above suggest that some sequence of (abnormal) operations can occur, suggesting in turn that some of the logic engine can function.
Reseating Socketed ICs
Another explanation for the abnormal behavior could be bad microcode or RAM.
The ROM and RAM chips are in sockets and corrosion can develop at the pin-socket junctions. It is a simple matter to remove and reseat all of these ICs. Inspection did not reveal any significant corrosion and the machine function was exactly the same after this procedure.
Further Diagnosis
Microcoded machines present a difficult problem at this point. The main symptom is ‘doesn’t work’ and the incorrect displays noted above give little or no further diagnostic information.
Board-swapping is a useful method of fault localisation if known good boards are available.
The DoPECC ROM emulator is a very valuable tool in this situation because it is loaded with a series of diagnostic microcodes that test well-defined machine elements in a well-defined sequence. A procedure can be laid out that begins with single-instruction microcodes and proceeds through a sequence that tests more and more of the machine. This prodedure is documented in the Wang 600 Fault Finding resource that can be found in the Wang Data section.